This invention relates to methods and apparatus for installing threaded inserts into a substrate. Such substrates, for example, include films, sheets or plates that may be curved or flat. The substrates may be made of materials such as metal, wood, glass, ceramic, cellulose, leather or plastic and may be completely solid, or partly porous, e.g. in the form of textiles or foam. More particularly, the invention concerns an insert that has a hollow shaft having first and second end portions and an intermediate portion between the end portions and a flange surrounding the first end portion. The insert is installed by passing the intermediate portion and second end portion through a hole in the substrate to preferably, but not essentially, pass through a rear surface of the substrate so that the flange of the insert contacts a front surface of the substrate. The second end portion is then pulled toward the first end portion to collapse the intermediate portion of the shaft upon the rear surface of the substrate (or upon the sidewalls defining the hole in the substrate) to form a gripping structure that secures the insert.
Inserts, as described above, are well known. They are for example readily purchased at local hardware stores for insertion into drywall substrates. Such inserts have more recently been used in production processes to provide threaded structures in substrates that may not be strong enough by themselves to support reliable threads or to reduce production time by eliminating the need to thread individual holes in the substrates with taps.
The use in production has, however, been hampered by the lack of processes and equipment to rapidly and reliably install such inserts.
The first, and still most common, way to install such inserts is by placing the shaft through a hole in the substrate, as above described, and turning a threaded rod with an end flange, e.g. a bolt having a bolt head or flanged threaded mandrel or screw head, into the threads in the second end of the insert thus pulling the second end toward the first end of the insert to collapse the intermediate portion of the insert, as previously described.
Such a method of installation has numerous disadvantages. For example, when the threaded rod with its end flange is turned to collapse the intermediate portion, significant torque is required. The high torque tends to turn the entire insert which can result in a bad installation by causing the formation of a defective gripping structure, or destroying or damaging the substrate or even more commonly, causing failure of threads within the insert. Great care must therefore be taken to assure that the insert does not spin. This often requires that a separate insert retaining means be employed that can withstand the required high torque. Even in such cases, the failure to obtain a good installation is more frequent than can be tolerated by many, if not most, production systems.
More recently, such inserts have been installed in production systems by threading a mandrel into the insert and longitudinally pulling the second end of the shaft of the insert toward the first end of the shaft of the insert, without applying a rotational torque. Nevertheless, the apparatus and processes for accomplishing that result have not been as reliable as desired. In particular, in existing apparatus, when the mandrel was pulled, it was necessary to move the entire drive assembly with the mandrel thus preventing secure attachment of the drive to a cylinder housing for the piston providing the pulling force. As a result, the drive (motor) tended to at least partially move rotationally when it was activated creating wear and misalignment and preventing smooth rotational operation. Further when the drive was activated to rotate the drive shaft, due to wear, as previously described, unacceptably high friction resulted between the drive shaft and piston through which the shaft passed, wearing both the drive shaft and the race or bore through the piston accommodating the drive shaft. As a further result, the turning of the drive shaft tended to also rotate the piston creating wear in the piston seals. The same increase in friction caused an increase in torque requirements to overcome friction losses. All of these problems resulted in significant down time and potentially unsatisfactory installation of the insert. As an even further disadvantage of such apparatus and methods, there was no good way to detect when the screw head (e.g. threaded mandrel) was withdrawn to permit positioning of an insert for loading onto the screw head. There was also no good way to detect where the screw head was screwed into the insert so that the nose retainer contacted the flange of the insert or where the shaft of the insert was inserted into the substrate so that the insert flange contacted the first surface of the substrate or where the screw head had been completely unscrewed from the insert. Accurate use of detectors would have been hampered in such devices due to motion of the drive relative to the cylinder housing and also due to lack of a secure attachment of the drive, the tendency of the piston to rotate and undesirable wear, as previously described. Attempts to stop the piston from rotating themselves give a further wear point as the misalignments due to the insecurely attached drive permit rotational forces to be applied to the piston to be at least partly successful in causing piston rotation due to wear as previously described. The devices further did not lend themselves to safe placement of detectors, i.e. there was no good way for internal detecting mechanisms and the required undesirable movements previously described caused vibration of any sensors used.